Whirlpool-type baths have long been employed to treat discomfort resulting from strained muscles, joint ailments and the like. More recently, such baths have been used increasingly as a means of relaxing from the daily stresses of modern life. A therapeutic effect is derived from bubbling water and swirling jet streams which create an invigorating motion to massage the user's body.
To create the desired whirlpool motion and hydromassage effect, jet fittings are typically employed to inject water at a high velocity into a receptacle, such as a bathtub, spa or therapy tank. Usually, the jet fittings are adapted to aspirate air so that the water discharged into the receptacle is aerated to achieve the desired bubbling effect (see, for instance, U.S. Pat. Nos. 4,593,420 and 4,742,965).
To enhance the whirlpool motion, some jet fittings aspirate water from the receptacle, thereby increasing the discharge rate of the fitting and hence the circulation of the water contained in the receptacle. Henkin et al. U.S. Pat. No. 4,689,839 discloses such a jet fitting which (i) draws spa or tub water into a mixing tube for entrainment with a primary stream of water, (ii) aerates the combined streams in a second mixing tube, and (iii) discharges the air/water mixture into a tub through a discharge nozzle. Because the mixing tube is mounted externally of the tub and remote from the fitting, the entrainment and aeration processes occur outside of both the fitting and the tub, thereby requiring extra plumbing to convey water to and from the mixing tube. Another disadvantage involves the location of the entrance to the mixing tube, which entrance is at a height well above the discharge nozzle, but below the level of water in the tub. Therefore, water entrainment will not occur if the level of the tub water falls below the level of the entrance to the mixing tube.
Another type of hydrotherapy jet assembly, suitable for mounting in a wall of a spa, bathtub or the like, is disclosed in Henkin et al. U.S. Pat. No. 4,731,887. The jet assembly of the Henkin et al. '887 patent includes a mixing chamber which is supplied with water under pressure by a water jet nozzle. A passageway extends internally through the assembly between the mixing chamber and the spa or tub so that water can be drawn from the spa or tub for entrainment by the water jet. Thus, the stream discharged from &:he jet assembly into the spa or tub includes the following components: (i) water supplied under pressure into the mixing chamber by the water jet nozzle; and (ii) water drawn or aspirated from the spa or tub for entrainment by the water jet.
The jet assembly disclosed in the Henkin et al. '887 patent can be adapted to draw or aspirate air, as well as spa or tub water, into the mixing chamber. However, in such an adaptation, it is difficult to strike a suitable balance between the amount of aspirated spa or tub water, on the one hand, and the amount of aspirated air, on the other hand, due to the fact that an increase in the quantity of aspirated water results in a decrease in the quantity of aspirated air and vice versa. Thus, in order to ensure that the jet nozzle can create a vacuum which, in turn, creates enough suction to entrain both air and water, the jet assembly of the Henkin et al. '887 patent is very limited with respect to the flow and pressure conditions under which it will perform satisfactorily, if at all. A delicate and impractical balance therefore exists between the size of the passageway for the entrained spa or tub water and the flow of aspirated air, both of which are a function of the size of the jet nozzle. Accordingly, if built on a commercial scale for use with a standard size pump typically employed in the hydrotherapy industry, the jet assembly disclosed in he Henkin et al. '887 patent would not work properly, if at all. In fact, the passageway for the entrained spa or tub water must be almost completely closed; or, otherwise, air could not be aspirated.
Still another type of jet fitting, also suitable for mounting in a wall of a spa, bathtub or the like, is disclosed in pending U.S. patent applications Ser. No. 322,653 filed Mar. 13, 1989, and Ser. No. 329,653, filed Mar. 28, 1989, both of which are owned by the assignee of the present application. The jet fittings disclosed in these copending applications employ two nozzles which coact to form a "jet pump" effect. The jet pump creates a low pressure condition which effectively sucks a secondary stream of spa or tub water from the spa or tub into a mixing chamber for entrainment with a primary stream of water. An air supply tube extends into one of the nozzles such that the combined water streams flow around the air supply tube and thereby create a low pressure condition which sucks air into the mixing chamber for entrainment with the combined water streams. The air/water mixture is discharged into the receptacle. Although this jet fitting can function with a standard size pump, the air supply tube partially blocks the flow of the air/water mixture as it is discharged into the receptacle, thereby reducing the efficiency of the fitting.
A problem common to all of the known jet fittings adapted to aspirate air and water is that the air sucked into the mixing chamber can not be regulated independently of the water. Air cools off the water with which it is entrained. The air/water mixture, in turn, cools off the spa or tub water as it is discharged into the receptacle. For certain applications where the temperature of the water must be hot, the inability to regulate the aspirated air makes the aeration process undesirable.